1. Field of the Invention
This invention relates generally to loudspeakers, and more particularly, to a novel structure of a loudspeaker designed to drive the node portion of a diaphragm which vibrates in its divided vibration mode by moving such node portion to a suitable location without changing the radiation area of the diaphragm. This invention also relates to a method of bonding the diaphragm to an edge member of the loudspeaker frame.
2. Description of the Prior Art
In conventional loudspeakers having a planar diaphragm, there is typically employed a nodal driving system which is designed to drive the node portion of a diaphragm vibrating in its low-order divided vibration mode so as to bring the divided vibration mode of the diaphragm to a higher frequency range.
These loudspeakers generally have a planar diaphragm whose front and rear surfaces are of equal area. Since the vibration mode is determined by the radiation area, that is, the surface area of the diaphragm, the size of the voice coil for driving a node portion of the diaphragm in its divided vibration mode is also determined by the radiation area of the planar diaphragm.
In such conventional loudspeakers, the diameter of the voice coil is naturally larger if the diaphragm surface area is greater, and this necessitates a correspondingly large structure for of the magnetic circuit, frame and other associated elements, so that the production of such loudspeakers is subject to extensive structural restrictions and elevated costs.
Also, in conventional loudspeakers, the peripheral edge of the diaphragm is cut vertical to the vibration plane, that is, transverse to the direction of thickness thereof. Thus, attaching the diaphragm to the correspondingly shaped edge member for securing the diaphragm to the frame, the adhesive used for this purpose often contacts and sticks to an unintended portion of the diaphragm or is often forced out from the bonded portions as the peripheral face of the diaphragm slides against the internal face of the edge member. In order to avoid such problems, the prior art expanded the edge member prior to attachment or used a non-tacky adhesive. Further, by using a planar diaphragm of a honeycomb sandwich structure, a rough trembling sound is often produced, because of the force or interaction of the layers of the honeycomb core, when the diaphragm vibrates, unless secure adhesion is made between the planar diaphragm and the edge member. Moreover, sufficient pressure must be applied to the joined area of the edge member and diaphragm because the adhesive may undergo a so-called slimming phenomenon when it sets.